Decoupling capacitors have been used with increases in processing speed of integrated circuits. Decoupling capacitors are required to have low ESL (Equivalent Series Inductance). As a decoupling capacitor satisfying this requirement, there has been known a thin film capacitor having a capacitor portion which is formed on a Si substrate by a thin film technique such as a sputtering or sol-gel method.
Such a thin film capacitor is coated with a protective layer composed of a resin material for mechanically reinforcing a capacitor portion. For example, Patent Document 1 has proposed a thin film capacitor including a capacitor having a dielectric layer composed of a metal oxide and a protective insulating layer composed of a resin material, a barrier layer composed of a nonconductive inorganic material being provided between the capacitor and the protective insulating layer.
As shown in FIG. 4, the thin film capacitor of Patent Document 1 includes a Si substrate 101, a capacitor 109 having a lower electrode layer 102, a dielectric layer 103 composed of barium strontium titanate (referred to as “BST” hereinafter), and an upper electrode layer 104, which are formed in order on the Si substrate 101, a barrier layer 105 formed to cover the capacitor 109, a protective insulating layer 106 formed on the barrier layer 105 and composed of a resin material, electrode pads 107, and bumps 108.
The barrier layer 105 is provided for preventing the dielectric layer 103 composed of BST from being reduced with moisture released from the resin material contained in the protective insulation layer 106. Examples of a material preferably used for forming the barrier layer 105 include amorphous materials, such as silicon nitride (Si3N4), aluminum oxide (Al2O3), silicon oxide (SiO2), and amorphous BST.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-214589
However, in the thin film capacitor described in Patent Document 1, the barrier layer 105 composed of an amorphous nitride such as amorphous silicon nitride may diffuse nitrogen atoms toward the dielectric layer 103 through the upper electrode layer 104 to change the composition of BST, thereby failing to obtain desired electric properties.
Also, the barrier layer 105 composed of amorphous aluminum oxide or amorphous silicon oxide may diffuse aluminum or silicon toward the dielectric layer 103. Therefore, such a material is undesirable.
Further, heat treatment is required for thermally curing the resin constituting the protective insulating layer 106. However, the barrier layer composed of an amorphous oxide such as amorphous BST causes the problem that the amorphous oxide takes oxygen away from the dielectric layer 103 through the upper electrode layer 104. Consequently, the composition of the dielectric layer 103 is changed, thereby failing to achieve desired electric properties. This is because an amorphous oxide is generally assumed to have the oxygen content smaller than the stoichiometric composition. Thus, oxygen is taken away from the dielectric layer 103 of crystalline BST having a higher oxygen content than that of the amorphous oxide. The barrier layer 105 composed of crystalline BST, not amorphous BST, does not cause the problem as described above. However, as described in Patent Document 1, the barrier layer 105 composed of crystalline BST can produce substantially no barrier effect.
After all, in the invention described in Patent Document 1, the properties of the dielectric layer 103 may be degraded by providing the barrier layer 105.